Method and apparatus for the synchronized control of two hydraulic drives

ABSTRACT

Two reversible hydraulic drives, e.g. for operating ship&#39;&#39;s stabilizing fins, are supplied by a single hydraulic feed pump. A pipeline connecting the drives is maintained at a settable pressure level, and lack of synchronism between the drives, manifested by a variation in pressure in that pipeline, is automatically corrected by a feed of pressure oil to, or a bleeding of pressure oil from, the connecting pipeline.

United States Patent Inventor Heinz-Gunter Ehluss Neuendercherweg 72, Tornesch/Holstein. Germany Appl. No. 859,888 Filed Sept. 22, 1969 Patented July 27, 1971 Priority Sept. 25, 1968 Germany P 17 76 120.5

METHOD AND APPARATUS FOR THE SYNCHRONI'ZED CONTROL OF TWO HYDRAULIC DRIVES 5 Claims, 4 Drawing Figs.

05. Cl 60/52 VM, 60/97 E, 9l/4ll R Int. Cl ..F1Sb 11/22 Field of Search...... 60/97 E,

[56] References Cited UNITED STATES PATENTS 3,070,959 1/1963 Giampapa et a1]. 60/97 E 3,359,870 12/1967 Purcell 60/520 M x 3,363,418 1/1968 Hbl6[al.... 60/97EUX 3,435,616 4/1969 Waldorff 60/97 E Primary Examiner- Edgar W. Geoghegan Attorney-Stevens, Davis, Miller & Mosher PATENTEU JUL27 I97! 3,595,019

SHEET 1 [1F 2 Fig. 2

sum 2 OF 2 PATENTED JUL27 IBYI fig. 1

METHOD AND APPARATUS FOR THE SYNCHRONIZED CONTROL OF TWO HYDRAULIC DRIVES BACKGROUND OF THE INVENTION The invention relates to a method and an apparatus for the synchronized control of two hydraulic drives with reversing, rotary or rectilinear motion in relation to one another in the same or opposite direction. The two drives are separated in space, the motion characteristic of one of the drives can be controlled either by a follower control or by hand.

In apparatus of this kind which for reasons of simplification has only a single controlled pump-unit for two hydraulic drive points which are separated from one another, the drives, e.g. hydraulic cylinder or torsional drives are connected in parallel or in tandem and supplied, for example, with oil under pres sure. Because, there can never be the same conditions prevailing at both consumer points with regard to leakage of pressure oil at the seals and to differences in loading, it is necessary to employ a supplementary synchronizing device to equalize the drive point not constituting a return control circuit with the pump unit, with the first operated drive point. Care has to be taken that the technical expenditure on synchronizing systems does not reach that for the possible equipping of the second drive point with its own pump unit and its own follower control.

In the case of hydraulically operated stabilizers for ships, which have fins projecting laterally from the ship's hull, it is known that in types having only one pump unit the unit usually has two separate axial piston pumps which are adjusted by a common control mechanism. The pump positions for each fin drive are controlled by the respective return control systems with mechanical return by rod linkage or cables.

In other applications for dual drive, not operating with sequential controls, double-flow pumps or volume dividers are used, for example in driving two parallel-running cylinders, and the parallel running is guaranteed by mechanical motion comparison and automatic release of pressure oil on the side which is operating faster at any given time. There is no precise control of the velocity of the cylinder movement however.

It has been the practice hitherto to transmit the motion of the driven drive to the controlled drive, this being effected where distances are short by mechanical means, e.g. by shafts or rod linkages, and where distances are longer and there is no possibility of direct transmission, by means of auxiliary power, e.g. by electric transmission. Both movements are then utilized, as already mentioned, for controlling two pumps, or the differences in motion representing errors, after appropriate amplification or conversion into other energy forms,'are used for controlling auxiliary valves.

Mechanical transmission means are only suitable if the two drives are a short distance apart and in most cases they require a definite arrangement of the units to be connected in relation to one another. Furthermore, on account of energy conversion and amplification with auxiliary energy, for example electrical transmission, it is not advantageous from the expenditure point of view.

Furthermore the use of two pumps in one pump unit is disadvantageous from the point of view of drive and pump control, as compared with the use of only one pump with a higher working pressure. Moreover, with double-flow pumps and parallel running of both drives and the use of auxiliary bypass valves, it is not possible to obtain a precise sequence control of the consumption points in relation to velocity and travel.

It is a main object of the invention to operate two hydraulic drives with reversing motion with one pump unit, which has only one single pump, e.g. a hydraulic pump, and to associate the motion of both drives to a follower control which has a return control system with only one of these drives.

SUMMARY According to the invention a method of synchronized control for two reversible hydraulic drives with a single hydraulic feed pump which is provided with a follower control which affects the movement of one of the two drives, and in which the pump and the hydraulic drives are connected in series is characterized by a hydraulic control system through which, in the event of lack of synchronism between the two drives, the motion of the drives generates pressure pulses by means of which, when a definite and adjustable pressure value is exceeded in the communication path between the two drives, an amount of fluid corresponding to the error in synchronism is fed in or drained off.

In one embodiment of the method according to the invention the middle positions of one drive and the other are used as the starting point for the generation of'pressure pulses.

in another embodiment of the method according to the invention each one of the drives can move a control piston in each direction of movement, whereby the drive which is not controlled displaces into a connecting pipeline a quantity of a hydraulic medium which is under initial pressure, while the control piston of the controlled drive takes up a quantity ofa hydraulic medium from the pipeline.

The method according to the invention can be put into practice by a technical construction of the invention in such a way that if a pressure level, which'is conveniently adjustable, in the pipeline is exceeded a replenishing valve or a draining valve is operated which, depending on the direction of the error (leading or lagging of the noncontrolled drive), increases the volume of hydraulic fluid enclosed between the two drives from the pump pressure line, or reduces it by drainage.

Here, according to a further embodiment of the invention, the volume equalizing process can take place for each direction of movement of the drive from the midway positions of an oscillatory movement and during the return movement of the control piston to the midway position an exchange of the hydraulic fluid takes place by drainage from a chamber, e.g.' by way of an overflow valve.

The invention is directed, furthermore, to apparatus for carrying out the method, especially for torsional movements about a central axis, in which two groups of control pistons can be driven mechanically in each case by one of the hydraulic drives and on the shaft of each of the drives there is a control arm provided, which is connected with an adjusting pin, also a stop, in which arrangement after each passage of the control arm, one of the pistons of the group of control pistons remains stationary and the second is carried along.

The synchronization control system is accordingly so designed that each of the two hydraulic drives, on its reciprocating travel, entrains two small. operating pistons. On passing through the midposition towards one side one piston in each case is thereby carried along with the travel of the drive and on returning to the middle is stopped again, whereupon the second piston is carried from the middle to the other side. An oil chamber of the piston of each drive is connected with the oil chamber of the piston of the other drive by means of a pipeline. Thus the connections of the two groups of pistons are opposite when the reversing movements of the drives are in the same direction and they are crossed when the movements of the drives are in opposition.

Furthermore, the pistons which correspond by way of the connecting pipeline are associated in such a way that a piston which is carried along from the center of movement of the noncontrolled drive displaces a small amount of oil and pushes it through the connecting pipeline to the controlled drive; here the associated piston takes up, from the midposition onward, an amount of oil which is normally the same.

When both drives pass through the midposition simultaneously and then remain in synchronism, the pressure in the communicating space between two pistons remains at an initial value which is supplied by the pump unit by way ofa check valve.

In the event of a leading error in the noncontrolled drive this would in the first place pass through the midposition earlier and furthermore displace more measuring oil then can be taken up at the controlled drive. The oil pressure rises above the initial value and opens a small valve which is connected to the communicating pipeline between the tandem-connected drives until the communicating volume has returned to its normal value.

A special feature of this synchronization control is the fact that the communicating pipeline between two pistons in each case is the transmitting element for the movements of the noncontrolled drive, and also the measuring point of the synchronization error, and indicator of the adjustment value for the equalization of the running error.

The invention further comprises the cooperation of check valves and small pressure relief valves and the association of the replenishing and drainage processes for the connecting pipeline of the series-connected drives.

For reasons of simplification the synchronization system which is necessary for the precise synchronism of the two drives must be constructed without any connection with the contro'i. It must have no mechanical transmission components from one drive to the other, it must also permit control over fairly long distances, and as measurement transmitter and energy carrier, must use the hydraulic oil and the oil pressure of the hydraulic unit of the controlled drive.

The uses of the invention include in particular the hydraulic adjusting gear of ships fin stabilizers, the steering gear of heavy land vehicles, large plate shears and folding presses with widely separated working cylinders.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows in diagrammatic form a circuit for synchronization control, in combination with a known seriesconnection ofa hydraulic pump with an oil feed which can be controlled and reversed in direction, with two torsional drives in the form of vane-type motors, and

FIGS. 2 to 4 show details of the circuit.

DESCRIPTION OF THE PREFERRED EMBODIMENT The follower control for a pump 1 in conjunction with a controlled drive 2 is not represented, neither are the hydraulic auxiliary elements for the pump 1, for example pressure relief and replenishing suction valves which is themselves are already known.

The drives 2 and 3 in the form of torsional drives, shown as vane-type motors, are mechanically connected with control blocks 4 and 5. These contain controlled pistons 6 and 7', 8 and 9. The pump 1 delivers pressure oil into a pipeline 10. The drive 3 then rotates in the direction of the arrow and the drive 2, which is connected with the drive 3 by a pipeline l1, likewise in the direction indicated by the arrow. Displaced return oil flows back to the pump by way of a pipeline 12. Each of the drives 3 and 2 operates by virtue of the pressure drop between the pipelines I and I2. If this is equal for both drives the pressure in the pipelines I0, 11 and 12 is in the ratio 2:1:0.

Levers 13 and 14 (FIGS. 2 and 3) are driven respectively by the rotation of the drives 3 and 2 and push the pistons 7 and 8 outwardly from the middle. Shortly before, as the levers moved from the angular position to the middle, the piston chambers 15 and 16 were placed under initial pressure by the working pressure in the pipeline by way of check valves 17 and 18. A piston chamber 19 in which fluid pressure acts on a larger area of the piston 7 is subjected to the working pressure by way of a pipeline 20 from the pipeline 10.

This ensures that before passing through the middle into its starting position the piston 7 is pu hed so as to make contact with a stop 21. The oil which is thereby displaced from the chamber increases its pressure for a short time above the initial pressure, closes a check valve 22 and escapes through an overflow valve 23 into a hydraulic fluid tank 24. Finally if the drives 3 and 2 pass through the middle in the direction of the arrow indicated on each of these drives, the piston 8 displaces oil while the piston 7 takes up oil. An error of lead in drive 3 over drive 2 increases the pressure in a pipeline 25 with the result that a spring-loaded valve 26 is opened in proportion to the error and pressure oil passes from the higher level of pressure in the pipeline 10, by way of a check valve 17, the valve 26 and a pipeline 27, into the lower pressure level of the pipeline 11. This normalizes the insufficient volume in pipeline 11 again, i.e. the drives 3 and 2 move apart from one another.

Any possible lag in drive 3 in relation to drive 2 is not corrected in this phase. After the change of direction of the pump delivery (pressure oil in pipeline 12, return oil in pipeline 10), the lag appears as a lead of drive 3 over drive 2 and is then equalized from the center of motion by the operation of a valve 28. This valve 28 then lets excess oil pass out of the pipeline ll into the tank 24.

The adjustment pressures of the valves 23 and 29 as well as of the valves 26 and 28 are chosen so that the vales 26 and 28 only react to a pressure slightly higher than the maximum working pressure, but the valves 23 and 29 have a response which is even higher than the maximum response pressure of the valves 26 and 28.

For the execution of the swinging motion of the lever arms I3 and 14, on which each group of pistons is actuated by one of the hydraulic drives, a lever 30 or 31 respectively is driven by the drive axle and with its adjusting pin 32 brushes past the stop 21 without making contact, whereby after every passage past the stop 21 a measuring piston remains stationary and the other is carried along. The pistons of the noncontrolled drive are formed of solid cylinders with a circular end face, whereas those of the controlled drive are stepped the cross-sectional area of one annular surface being equal to the cross-sectional area ofone circular face (FIGS. 2 and 3).

The special advantages of this synchronization control are manifested in the possibility of very precise movement of the second reversible drive, which is not governed by the control system, even where the distances are fairly large and the space conditions difficult. Any substantial errors due to the compressibility of the oil in the measuring chambers and communication pipelines are avoided by the placing of the oil under an initial pressure. Inevitable errors due to small amounts of leakage oil from the measuring pistons cannot accumulate because as the pistons pass through the midpoint at any time the control process starts again with a fresh original position. The synchronization control system operates with simple constructional elements of general oil-hydraulics and is supplied direct from the main hydraulic unit with pressure energy and new, filtered oil.

Further inherent features of the invention are devices for the execution of the method having two reversing rotary drives with swing angles of up'to about :60".

Iclaim:

I. A method of synchronized control for two reversible hydraulic drives with a single hydraulic feed pump which is provided with a follower control which affects the movement of one of the two drives, the pump and the hydraulic drives being connected in series, comprising providing a hydraulic control system for synchronization of the drive means in which this synchronization control means, in the event of lack of synchronism between the two drives, actuated by the motion of the drives generates pressure pulses which cause feeding in or draining off of an amount of fluid corresponding to the error in synchronism into the communication path between the two drives, and when passing through the midpositions of one drive these midpositions are utilized as the starting point for the generation of pressure pulses.

2. A method as claimed in claim I, in which each of the drives can move a control piston in each direction of movement, whereby the drive which is not controlled displaces into a connecting pipeline a quantity of a hydraulic medium which is under initial pressure, while the control piston of the controlled drive takes up a quantity of hydraulic fluid from the pipeline.

3. A method as claimed in claim 2, in which if an adjustable pressure level in the pipeline is exceeded a replenishing valve or a draining valve is operated to correct the error by increasing the volume of hydraulic fluid enclosed between the two drives from the pump pressure line, or to reduce the volume by drainage.

4. A method as claimed in claim 3, in which the volume equalizing procedure for each running direction of the drive takes place from the midpositions of an oscillatory movement andduring the return motion of the control piston to the midposition there is an exchange of the hydraulic fluid through discharge from a chamber by way of an overflow valve.

5. Apparatus for synchronized control of two reversible hydraulic drives, both fed in series by a single pump, comprising a follower control which affects the movement of one of the drives said control having two groups of control pistons, each driven mechanically by one of the hydraulic drives, an actuating arm and associated adjusting pin driven by each drive, a stop, said arrangement being such that after each passage of an actuating arm one of the pistons of a group remains stationary and the other is moved. 

1. A method of synchronized control for two reversible hydraulic drives with a single hydraulic feed pump which is provided with a follower control which affects the movement of one of the two drives, the pump and the hydraulic drives being connected in series, comprising providing a hydraulic control system for synchronization of the drive means in which this synchronization control means, in the event of lack of synchronism between the two drives, actuated by the motion of the drives generates pressure pulses which cause feeding in or draining off of an amount of fluid corresponding to the error in synchronism into the communication path between the two drives, and when passing through the midpositions of one drive these midpositions are utilized as the starting point for the generation of pressure pulses.
 2. A method as claimed in claim 1, in which each of the drives can move a control piston in each direction of movement, whereby the drive which is not controlled displaces into a connecting pipeline a quantity of a hydraulic medium which is under initial pressure, while the control piston of the controlled drive takes up a quantity of hydraulic fluid from the pipeline.
 3. A method as claimed in claim 2, in which if an adjustable pressure level in the pipeline is exceeded a replenishing valve or a draining valve is operated to correct the error by increasing the volume of hydraulic fluid enclosed between the two drives from the pump pressure line, or to reduce the volume by drainage.
 4. A method as claimed in claim 3, in which the volume equalizing procedure for each running direction of the drive takes place from the midpositions of an oscillatory movement and during the return motion of the control piston to the midposition there is an exchange of the hydraulic fluid through discharge from a chamber by way of an overflow valve.
 5. Apparatus for synchronized control of two reversible hydraulic drives, both fed in series by a single pump, comprising a follower control which affects the movement of one of the drives said control having two groups of control pistons, each driven mechanically by one of the hydraulic drives, an actuating arm and associated adjusting pin driven by each drive, a stop, said arrangement being such that after each passage of an actuating arm one of the pistons of a group remains stationary and the other is moved. 